Under P.L. 90-602, "The Radiation Control For Health and Safety Act of 1968", manufacture and accountability for X-ray system performance is deemed to be contingent upon the ability of the AC power supply to meet the equipment's minimum requirements as specified by the manufacturer. The greatest demand on the AC supply occurs during a radiographic exposure, usually at the highest current setting, and the highest kilovolt peak (kVp) setting permitted at that current by X-ray tube cooling characteristics. To prevent overheating of the tube at this setting, exposure time must be short. Thus, in evaluating the adequacy of the AC source under worst case conditions, the test instrumentation used must have a fast response.
Previously, peak voltmeters have been used to measure the surge voltage. However, these instruments have proved to be unsatisfactory because they do not measure the minimum voltage. Oscilloscopes and special preamplifier-strip chart recorder combinations may have storage facilities, high accuracy, and fast response, but their resolution is low and their bulkiness usually precludes portability. Digital voltmeters have high resolution and accuracy but show a very slow response.